In the art of boring subterranean boreholes for pipelines, such as pipelines used in the underground transportation of natural gas, debris and any lost or foreign materials in the borehole should be removed prior to installation of the pipeline. Such boreholes, typically called "directional horizontal" boreholes, are substantially horizontal and are drilled in a particular direction toward a certain destination, in contrast to vertical boreholes deadening into the subterranean formation as typical for boreholes for oil and gas production wells.
The substantially horizontal position of boreholes for pipelines makes removing debris and lost materials from the boreholes difficult, costly, and time consuming, to an extent even greater than is common for retrieving lost materials from oil and gas wells. Tools for this purpose, commonly "fishing" tools borrowed from the oil and gas well drilling industry, typically depend on powerful magnets to recover the lost materials. Debris in pipeline boreholes, however, is not always comprised of metal that may be attracted by such magnets. Moreover, even if the debris is comprised of metal that might be attracted by the magnet, the forces of gravity pull against the forces of the magnet in a horizontal well, making such traditional tools less effective.
These problems with the traditional fishing tools have been noted as well in their use or attempted use to retrieve lost materials in slanted or horizontal boreholes drilled for oil and gas production wells.
In the art of drilling boreholes in hydrocarbon bearing formations to facilitate production of hydrocarbons from such formations, occasions sometimes arise that make it necessary or advantageous to drill at an angle or slanted direction rather than in a typical vertical direction. For example, slanting the lower end of a wellbore substantially horizontally so that it penetrates the "pay zone," or part of the formation to be produced, allows a greater number of perforations into that pay zone from that wellbore. This enables faster production from the formation.
Slanting a wellbore substantially horizontally and at considerable distance radially away from the drilling rig also enables the pay zone to be entered at a number of different locations radially spaced about the drilling rig so that a plurality of wellbores can be drilled from a common drilling location. This technique is especially advantageous when the cost of moving the drilling rig is considerable, as is often the case in offshore drilling.
Such drilling at an angle or slant, called "directional drilling," is also used when locating a drilling rig directly over the desired site is impractical or impossible because of a river, hill, or some other obstruction.
Sometimes while drilling such a well, drill bits or other tools may become lost in the wellbore. The cost of such tools and/or their interference with further drilling may make it desirable or essentially necessary to recover the lost tools.
New and improved tools and methods are needed for clearing debris and removing lost materials from slanted boreholes in the oil and gas well drilling industry and horizontal directional boreholes in the pipeline industry.